1. Field of the Invention
The present invention relates to a data interpolation processing apparatus incorporated into an ultrasonic diagnostic system.
2. Related Background Art
An ultrasonic diagnostic system has been used in which, upon bringing an ultrasonic transducer into contact with a subject, particularly the surface of the human body to be inspected, ultrasonic beams are emitted into the human body, wherein the ultrasounds reflected by tissue in the human body are received by the ultrasonic transducer while the inside of the human body is scanned with the ultrasonic beams, and a tomographic image of the interior of the human body is displayed on the basis of the received signals, thereby facilitating diagnosis of diseases of the viscera and the like of the human body.
As a scheme of scanning the subject with the ultrasonic beams, there are known, for example, a sector scanning scheme in which a great number of ultrasonic beams (scanning lines) fan out, a linear scanning scheme in which scanning lines extend in parallel with each other, and a convex scanning scheme using a probe in which ultrasonic transducers are arranged in a convex-like configuration.
The thus obtained received signals are subjected to a sampling process and also an A/D conversion so as to be converted into digital sampling data. However, generally, positions of the respective pixels represented by such digital sampling data do not correspond to positions of the respective pixels on a display screen of a CRT display device, for example, on which a tomographic image is displayed. Consequently, it is necessary to perform a data interpolation processing so as to generate indication data related to a coordinate system suitable for display.
FIG. 7 is a view useful for understanding the conventional data interpolation processing operation.
The straight lines extending from the upper left of the figure to the lower right denote scanning lines n-1, n, n+1, n+2, . . . , respectively. On the other hand, the straight lines extending horizontally denote lines m, m+1, . . . , respectively, each spaced apart in a scanning direction and representing an arrangement of sampling data involved in the same depth of the subject.
The sampling data correspond to the associated cross points of the scanning lines n-1, n, n+1, n+2, . . . , and the lines m, m+1, . . . , respectively. Specifically, to obtain indication data at the point T, the sampling data S(n, m), S(n, m+1), S(n+1, m) and S(n+1, m+1) are used at the adjacent four points S.sub.-- n.sub.-- m, S.sub.-- n m+1, S.sub.-- n+1.sub.-- m, and S.sub.-- n+1.sub.-- m+1, respectively. Now, as shown in FIG. 7, it is assumed that .DELTA.R denotes a distance between the line m and the line m+1; R.sub.err denotes a distance between the line m and the point T; .DELTA..theta. denotes a distance between the scanning lines n and n+1; and .theta..sub.err denotes a distance between the scanning line n and the point T.
First, in accordance with the following equation (1), the interpolation data T (n, m) at the point T.sub.-- n is obtained by means of implementing a linear interpolation processing using sampling data S(n, m) and S(n, m+1) at the two points S.sub.-- n.sub.-- m, and S.sub.-- n.sub.-- m+1, respectively, while the interpolation data T (n+1, m) at the point T-n+1 is obtained by means of implementing a linear interpolation processing using sampling data S(n+1, m+1) and S(n+1, m+1) at two points S.sub.-- n+1.sub.-- m, and S.sub.-- n+1.sub.-- m+1, respectively. ##EQU1## where k=n, n+1
Next, the indication data T (x, y) corresponding to the point T is obtained by means of implementing a linear interpolation processing based on the following equation (2) using the two pieces of interpolation data T (n, m) and T (n+1, m) obtained through the equation (1). ##EQU2##
The implementation of such an interpolation processing for the tomographic image in its entirety makes up a tomographic image adapted for display.
The interpolation processing scheme as mentioned above is called a bi-linear interpolation, and is well known.
According to the conventional interpolation processing scheme, however, it may happen that high luminance lines appear on the ultrasonic scanning lines, so that these artifacts are displayed in the form of a virtual image. Specifically, a recent ultrasonic diagnostic system is provided with a magnifying function for a displayed image. In the tomographic image obtained by the sector scanning scheme and the convex scanning, the scanning line density will become lower as the depth of the subject is greater, since the scanning lines substantially fan out. In this condition, if the linear interpolation processing is implemented, there will appear peaks of data on the scanning lines. As a result, it will cause the following drawback. That is, it may happen that the high luminance lines appear on the ultrasonic scanning lines. This high luminance line often appears when the linear interpolation is carried out with a larger value of ultrasonic sampling data.